The present invention relates to an improved ozonizer, and more particularly relates to improvements in a contact-type ozonizer having one or more discharge electrodes and one or more counterpart electrodes for ozonization of supplied gas via contact with a discharge field generated by the cooperating electrodes.
Ozonizers on the market are roughly classified into two major types, i.e., non-contact type ozonizers and contact type ozonizers. In the case of a non-contact type ozonizer, a discharge electrode is arranged out of contact with a dielectric whereas, in the case of a contact type ozonizer, a discharge electrode is arranged in contact with a dielectric. In both types of ozonizers, a material gas introduced into an ozonization chamber is ionized via contact with a discharge field generated by electrodes disposed in the chamber.
In construction of a typical conventional non-contact type ozonizer, a layer of counterpart electrode is formed via, for example, chemical deposition on the inner surface of a tubular dielectric, and this tubular dielectric is surrounded by a tubular discharge electrode while leaving an elongated cylindrical ozonization chamber in between. This ozonization chamber is provided at one longitudinal end with an inlet and at the other longitudinal end with an outlet for material gas. The discharge electrode and counterpart electrode are electrically connected to a common high voltage generator. A cooling chamber is arranged around the tubular discharge electrode and provided with an inlet and an outlet for a cooling medium such as water.
During operation, the high voltage generator applies high voltages to the electrodes in order to generate a discharge field within the ozonization chamber. A material gas such as air or oxygen is introduced into the ozonization chamber through the inlet. During travel from the inlet to the outlet the gas is ionized through contact with the discharge field within the ozonization chamber. Ionized gas is put out of the ozonization chamber through the outlet.
In order to assure appreciable ozonization of the material gas in such a non-contact type ozonizer, the relatively large distance between the discharge electrode and the counterpart electrode necessitates application of an extremely high voltage up to higher than 10 KV and, accordingly, requires use of a large sized voltage generator. In addition, the relatively large capacity of the discharge electrode tends to lessen operation of the cooling system, making it difficult to remove heat generated by the discharge field. The low cooling effect naturally results in low ozonization efficiency.
The contact type ozonizer was proposed in an attempt to remove such inherent drawbacks of the non-contact type ozonizer. In one typical construction of the conventional contact type ozonizer, a counterpart electrode is deposited on or embedded in one face of a thin planar dielectric and one or more discharge electrode foils are arranged on the other face of the dielectric. The electrodes are electrically connected to a common high voltage generator and the unit is encased within a housing to define an ozonization chamber for, as in the case of the non-contact type, passage of material gas. The operation is principally the same as that of the non-contact type.
Reduced distance between electrodes in this contact type allows use of relatively low voltage for generation of the discharge field and use of a small size voltage generator. Due to this advantage, the contact type has significantly penetrated into the marketplace. Despite this merit, the foil type discharge electrode is vulnerable to damage during long periods of use. In addition, direct contact of the discharge electrodes with the dielectric of relatively low thermal conductivity tends to incur continued presence of heat generated by discharge in the discharge field, thereby barring a further rise in ozonization efficiency.
Because of the foregoing, raising ozonization efficiency is the greatest demand in the field of gas ozonization. In an attempt to satisfy such a demand, use of a pulsatile voltage is proposed for generation of a discharge field. It was observed, however, that gas ozonization takes place only during the very short initial period of pulsatile voltage application and continued application of the voltage causes undesirable heat generation. In addition, when air or oxygen is used for the material gas, such heat generation is liable to cause production of harmful nitrogen oxides. Further, heat remaining in the discharge field in the ozonization chamber tends to decompose ozones once they are generated, thereby lessening the efficiency of total ozonization.
Considering ozonization is carried out during the initial period of pulsatile voltage application, it is also proposed to employ pulsatile voltage at high frequencies. Experimental tests have confirmed, however, that a rise in frequency lowers ozonization efficiency. This is believed to be caused by the fact that generation of heat by electric discharge is followed by subsequent discharge before its diversion to other locations and, as a consequence, heat accumulation takes place in the discharge field and newly formed ozones are destroyed by the subsequent discharge. In addition, use of pulsatile voltage at discharge is inevitably accompanied with vibration of the system which often causes destruction of the dielectric which is typically low in mechanical strength.